JavaScript Data Types

What Are the JavaScript Data Types?

Microsoft JavaScript has six types of data. The main types are numbers, strings, objects, and Booleans. The other two are null and undefined.

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String Data Type

Strings are delineated by single or double quotation marks. (Use single quotes to type strings that contain quotation marks.) A string is also an object in JavaScript, but it is a special case, with special properties. The following are examples of strings:

"The cow jumped over the moon."
'"Avast, ye lubbers!" roared the technician.'
"42"

A string can contain zero or more unicode characters. When it contains zero, it is called a zero-length string ("").

Number Data Type

JavaScript supports both integer and floating-point numbers. Integers can be positive, 0, or negative; a floating-point number can
contain either a decimal point, an "e" (uppercase or lowercase), which is used to represent "ten to the power of" in scientific notation, or both. These numbers follow the IEEE 754 standard for numerical representation. Last, there are certain number values that are special:

Octal integers are specified by a leading "0", and can contain digits 0 through 7. If a number has a leading "0" but contains the digits "8"
and/or "9", it is a decimal number. A number that would otherwise be an octal number but contains the letter "e" (or "E") generates an error.

Hexadecimal ("hex") integers are specified by a leading "0x" (the "X" can be uppercase or lowercase) and can contain digits 0 through 9
and letters A through F (either uppercase or lowercase). The letter "e" is a permissible digit in hexadecimal notation and does not signify an exponential number. The letters A through F are used to represent, as single digits, the numbers that are 10 through 15 in base 10. That is, 0xF is equivalent to 15, and 0x10 is equivalent to 16.

Octal and hexadecimal numbers can be negative, but cannot be fractional. A number that begins with a single "0" and contains a decimal point is a decimal floating-point number; if a number that begins with "0x" or "00" contains a decimal point, anything to the right of the decimal point is ignored.

Booleans

The possible Boolean values are true and false. These are special values, and are not usable as 1 and 0.

Note In a comparison, any expression that evaluates to 0 is taken to be false, and any statement that evaluates to a number other than 0 is taken to be true. Thus the following expression evaluates to true: